Begin First Challenge:
Assign numbers to student groups; then assign sample masses to each student group. Students will try to find the densities of the objects, and then use a table of values posted on the board to guess what their samples are made of.
Groups should use the following spreadsheet to record results:
File. Since this lesson plan is a teacher's copy, students can access this file by going to http://shodor.org/~rohins/portfolio and clicking on the link labelled "Density Table."
Teachers should compare the densities students derive with the densities on the file below: File
- Students will find volumes by using Archimedes’ Principle and dropping masses into beaker of water and measuring the difference in water level.
- Give a sample mass to each student group.
- Have each group fill a 100 mL beaker with enough water to cover the sample when inserted.
- Ask each group to record the water level before inserting the sample.
- Instruct the groups to slowly drop the sample mass into the water and record the new water level.
- Calculate the volume. Keep the measurements.
- Make a note as to whether the sample sinks or floats.
- Remove the sample, wipe it dry, and retain sample for further exploration.
- Discard water from the beaker and dry it out.
For the next step, use a 250mL beaker or another beaker of similar size. The instructor may elect to perform these steps far away from electronic equipment to minimize accidental damage due to water spillage.
For measuring the volume, the instructor can either use a container with incremental graduations or use a ruler to measure the water levels and compute the volume using the length and width of the container and the change in the height of the water level.
- Give students a 100 mL cylinder to use as a raft.
- Place the raft into a 250 mL graduated cylinder so that it floats and record the water level. This is the initial volume. (Make sure the sides of the rafts do not touch the sides of 250 mL cylinders because the friction will offset the true weight of the raft and interfere with measurements)
- Gently place the sample mass into the raft and record the new water level. This is the final volume.
- Remove the mass and raft from the water so that the next group can make measurements.
- Instruct the students to calculate the change in volume of the water by subtracting the initial volume from the final volume (Vfinal – Vinitial = Vdisplaced).
Now students should have the following data:
- Volume of mass submerged in water
- Volume of water displaced when mass was placed on raft
So, students can calculate density using the equation ρ = m⁄v or through the Excel sheet attached at the top of this page.
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